In a conventional cylinder and piston assembly, for example, for two-stroke engines with slot gas distribution, sealing is accomplished by resilient split rings (see Krouglov M. G., Combined Two-Stroke Engines, Moscow, Mashinostroenie, 1977, p.8).
The prior art, however, provides sealing only the annular gap caused by the presence of expansion clearance between a piston and a cylinder wall. With the slot gas distribution which is commonly used in the majority of two-stroke engines, the efficiency of such sealing is inferior as both the combustion products and the pre-compressed charge can flow between blowoff and exhaust ports through the annular gap around the piston, in particular, where the rings meet gas distribution ports. As in two-stroke engines the expansion clearance is relatively large, and increasing the cylinder diameter drastically contributes to the gap area to piston area ratio, the resulting enhanced loss of the fresh charge and increased residual gas ratio prohibit the attainment of high volumetric performance in the two-stroke engines having the cylinder of a diameter above 100 mm and the gas distribution ports arranged in the same lateral plane of the cylinder.
U.S. Pat. No. 2,208,782 discloses a cylinder and piston assembly for an internal combustion engine, comprising a cylinder with gas distribution ports separated by walls, a piston arranged in the cylinder and provided with at least a pair of sealing rings located in grooves and at least a pair of spring pressed elongate members located in the respective grooves on the piston cylindrical surface.
A disadvantage of the above prior art, most closely approaching the present invention, is that the elongate members do not lend themselves to sealing functions as they fail to mate the sealing rings.